This invention relates to intravenous needle assemblies and, more particularly, to a plug usuable with an intravenous needle for detecting the presence of the needle point within a blood vessel, and for preventing flow of blood from the assembly during the venous puncture procedure. The device provides for venting air rapidly, in order to enable the blood to flow from the blood vessel into a transparent blood-detecting chamber under venous pressure and in some cases more rapidly, than has been the case in the past, while at the same time preventing any blood flow through the vent passages.
During the placement of a needle or flexible catheter into a vein or other body member, it is desirable to determine whether or not the tip of the needle or catheter is properly situated within the vessel. Because the introduction of the assembly into the vein is normally accomplished by the use of an opaque rigid metallic needle, it is impossible to detect the presence of blood in the needle and needle hub.
Because of this, prior art introducer needles are equipped with a hub having a transparent flash chamber into which the blood flows to indicate that the needle point is properly placed. Many such devices, however, have leakage problems which cause blood flow over the hands of the user. It is important to avoid such circumstances, because of the potential for transfer of disease in exposure to blood from a patient. In providing a chamber with means for venting air therefrom so that the blood will flow rapidly into the chamber for indication of venous entry, the air vents have a tendency to leak.
With this invention, by contrast, a flashback assembly is provided with transparent walls to indicate the presence of blood in the hub of the assembly and that the needle has, indeed, entered the vein of a patient, with the vent being comprised of a required cross section of actual venting area, but with vent holes much smaller than those achieved in the prior art. This is arranged in accordance with this invention by the use of a laser for drilling the vent holes. By doing so, the laser provides the same or a greater cross sectional area of actual air venting, while at the same time providing holes which are small enough to prevent the leakage of blood through the air vents.
In accordance with this invention, a laser is used for drilling one or an array of small holes in the end of the flow control plug. The hole or holes comprise a total sufficient cross sectional area to provide flashback times at least equivalent or better than the prior art plugs utilizing other conventional venting methods such as membranes, sintered thermoplastics, or slit valves.
The laser utilized for drilling the holes may be, for example, a YAG laser (yttrium-aluminum-garnet). Also, a ruby laser may be utilized, but the YAG laser is preferred. The holes will have a diameter of less than 0.002 inches and, preferably, less than 0.001 inch. In this connection, it has been determined that holes of 0.003 inches or above in diameter leak blood at venous pressures.
In considering generally the conditions for carrying out the invention herein, it has been determined that conventional thermoplastic materials such as polyethylene do not absorb the laser beam wave length to the level required for producing the holes in accordance herewith, without containing an additive which increases absorption. Thus, it was found in accordance with this invention that an additive such as ACRA WAX.RTM. added to the material under consideration provides the proper absorption characteristics for plugs made in accordance with this invention. That is, it is important that when the holes are being drilled a proper level or degree of absorption of a laser wave length takes place in order to achieve vaporization of the material, and, hence, properly drilled holes. If the proper level is not obtained, melting of the material takes place with clogging of such small holes.
Thus, pellets of polyethylene were provided with a one percent quantity, by weight, of ACRA WAX.RTM. and extruded into ribbons of about 0.005 inches thick. Circular samples of this material were drilled with the YAG laser. A sample with three holes drilled in the sample with each hole of less than 0.002 inches in diameter were tested utilizing a dyed water to indicate the presence of the liquid in the plug of the invention. The test indicated not only rapid flashback time but an absence of leakage.
In considering further the conditions for carrying out the invention here, the following thermoplastic materials are representative of materials which may be utilized for formulating the plugs of the invention. These materials are polyethylene as indicated above, polypropylene, polyvinyl chloride, acrylonitrile butadiene-styrene terpolymer, polyethylene terephthalate and poly urethane. It will be understood that other materials may be used as long as they come within the operating parameters discussed herein. While most materials listed above will not have the appropriate absorption requirement necessary for laser drilling as discussed herein, it should be understood that some materials will, indeed, have those characteristics, thus eliminating the need for an additive for that purpose.
Examples of additives which may be used to increase the absorption properties of the thermo plastics utilized with the invention here include ADVAWAX 280.RTM., a product of Morton Thiokol, or ACRA WAX.RTM. C lubricant, a product of Glyco Incorporated, 488 Main Street, P.0. Box 5100 Norwalk, Conn. 06856. ACRA WAX is an alkyl amide which is the reaction product of ethylene diamine and stearic acid. The specific name is N,N'-ethylene bis(stearamide). The additive may be mixed with the resin at the rate of within the range of between about 0.5 and 5 percent by weight, and, preferably, within the range of between about 1.0 and 3.0 percent by weight.
In order to prepare the plugs of the invention, the following example indicates one representative procedure for making such plugs.